The retinal pigment epithelial cells (RPE) and the choriocapillaris (CC) have an intimate relationship in the eye. As nearest neighbors, separated only by Bruch's membrane, they rely on each other and assist each other in accomplishing their critical role of sustaining healthy photoreceptor cells. This proposal explores the relationship between these two cell types from the development or birth of choriocapillaris (5-23 weeks gestation) to the dysfunction or death of either cell type in two different forms of age-related macular degeneration (AMD), geographic atrophy (GA) and exudative AMD. The metabolic status and viability of CC will be evaluated using enzyme and immunohistochemistry (IH) and TUNEL labeling. RPE cell viability and function will be investigated with IH and TUNEL labeling. Growth factors (FGF's, VEGF, PIGF, angiopoietins, erythropoietin, stem cell factor, stromal derived factor-1) that the two cells types produce and use for themselves (autocrine) or their neighbor (paracrine), and their cognate receptors will be investigated by IH and bleaching of the tissue. Tube formation in vitro by fetal human endothelial cells in the presence or absence of fetal RPE will be assessed for paracrine and autocrine effects of growth factors using neutralizing antibodies and siRNA. The contribution of leukocytes and complement to CC death and dysfunction and to CNV in AMD will be investigated by IH to identify cell types, leukocyte numbers (nonspecific esterase, CD45, CD68), leukocyte adhesion molecules (ICAM-1, VCAM-1, P-selectin), and pro-inflammatory (TNFa, IL6, IL8, MCP-1) and angiogenic (FGF's, VEGF, PIGF, angiopoietins) cytokines. The spatial relationship between complement factor H, attack complex, leukocytes and CC viability will also be investigated. Using our alkaline phosphatase flat-embedding technique in which CC vascular density and percent of Bruch's membrane covered with RPE can be quantified, we have established and will continue to investigate the mutualistic symbiotic relationship between CC and RPE. This analysis will permit us to establish how this relationship is disrupted in GA and exudative AMD. The goal of this proposal is to better understand the relationship between these two neighboring cell types and elucidate important factors that could be targeted to maintain or improve this healthy relationship.